Scientific Forecaster Discussion

000
FXUS64 KLCH 180313
AFDLCH
Area Forecast Discussion
National Weather Service Lake Charles LA
913 PM CST Sat Feb 17 2018
.UPDATE...
As of 9 PM, radar and surface observations indicate the shallow
cold front has continued to progress southward and extends roughly
along Interstate 10. Reflectivity of the showers along the front
has decreased over the past several hours and short-term guidance
indicated further weakening of showers can be expected over the
next few hours. Therefore, PoPs have been decreased through the
rest of this evening.
Behind the cold front, temperatures have already dropped into the
upper 50s/low 60s. The inherited forecast indicated a slower
southward progression of the surface cold front and current
temperatures were already at or near forecast lows for the
evening. Radiational cooling and cold air advection should yield
additional cooling through the overnight hours and temperatures
have been decreased accordingly.
The rest of the inherited forecast remains on track with no
adjustments needed at this time.
&&
.PREV DISCUSSION... /issued 540 PM CST Sat Feb 17 2018/
AVIATION...
A front that has stalled over southeast Texas and southern La
this afternoon is producing sctd showers. Showers are moving to
the northeast. It appears that this boundary is again on the move
to the east. Ceilings are beginning to drop over srn La attm w/
ceilings and vsby better over se Tx. But se Tx and srn La will
see the same outcome w/ both ceilings and vsby becmg IFR/LIFR
twrds midnight hr. This will cont thru sr before a slowly
improving.
PREV DISCUSSION... /issued 401 PM CST Sat Feb 17 2018/
DISCUSSION...
A shallow cold front extends from near Natchitoches southwest to
near Lufkin where temperatures are in the mid 50s compared with
Alexandria which reported 74 degrees last hour. The front is
producing enough lift to spark scattered showers across the area
this afternoon. Expect these showers to sink further south through
the evening before the front stalls somewhere over the area.
Exactly where the front comes to rest may potentially wreak havoc
on overnight lows which are presently based on relatively little
CAA. Should the front advance to near the coast, this may need to
be revised. The front will lift back to the north Sunday as a warm
front which will be enough to sustain at least low end POPs early
Sunday before precipitation comes to an end Sunday afternoon.
Marine fog is once again expected to begin moving inland after
sunset this evening although the northward extent should be
limited to near the coast due to the boundary. Thus, opted to
forgo any inland dense fog advisories at this time. That said, areas
along the immediate coastline will likely see visibilities drop
to a mile or less. Fog should abate from land areas by mid
morning.
Guidance remains very consistent in bringing drier mid and upper
level air across the region Monday into early Tuesday which might
be enough to give the area a break from the mostly cloudy skies
that have been the hallmark of the last couple of weeks.
Another slow moving frontal boundary is progged to approach the
area late Tuesday. The GFS is the only reliable guidance actually
that actually pushes the front through the area while the
remaining guidance stalls the front over east Texas setting up a
prolonged period of potentially heavy rain. Following the majority
rule approach, I am inclined to lean the forecast towards the
stalling solution which will result in widespread showers and
thunderstorms beginning late Tuesday through Thursday. QPF values
were based on WPC's forecast and show widespread totals of two to
two and a half inches Tuesday through Thursday. Forecast soundings
also show more instability than we've seen recently indicative of
potentially stronger thunderstorms. However, given the
considerable model uncertainty, that is subject to change.
Jones
MARINE...
Widespread dense marine fog is expected to develop across the
nearshore coastal waters and coastal lakes and bays beginning
shortly after sunset this evening. Visibilities of less than a
mile area expected. Patchy dense fog will also be possible across
the outer coastal waters. The fog is expected to begin to
dissipate late Sunday as drier air works its way into the region.
&&
.PRELIMINARY POINT TEMPS/POPS...
AEX 52 71 60 77 / 30 20 10 10
LCH 58 73 62 75 / 30 10 10 10
LFT 60 75 64 78 / 30 10 10 10
BPT 60 73 62 76 / 30 10 10 10
&&
.LCH WATCHES/WARNINGS/ADVISORIES...
LA...None.
TX...None.
GM...Dense Fog Advisory until noon CST Sunday for GMZ430-432-435-450-
452-455.